Method of and apparatus for electric welding



N. WILKINSON.

METHOD OF AND APPARATUS FOR ELECTRIC WELDING. APPLICATION FILED JUNE 28, 1919. RENEWED MAR. 1,1920.

di /x UNITED STATES PATENT OFFICE.

NATHAN WILKINSON, OF WAUWATOSA, WISCONSIN, ASSIGNOR TO ALLIS-CHALMERS MANUFACTURING COMPANY, OF MILWAUKEE, WISCONSIN, A CORPORATION OF WISCONSIN.

METHOD OF AND APIARATUS I EOR ELECTRIC WELDING.

Original application filed August 27, 1914, Serial No. 859,121.

Specification of Letters Patent.

1919, Serial No. 307,803. Renewed March 1, 1920. Serial No. 363,097.

To all whom it may concern:

Be it known that I, NATHAN \VILKINsoN, a citizen of the United States residing at VVauwatosa, in the county of Milwaukee and State of lVisconsin, haveinvented certain new and useful Improvement in Methods of and Apparatus for Electric Welding, of which the following is a specification.

This invention relates in general to a method of and apparatus for assembling and constructing structures constituted, at least, in part, of an element of electrically con ductive material of comparatively poor mag netic qualities and comprising portions autogeneously united or welded together, the welded portions being electrically connected through means other than the welded surfaces of the portions and has particular relation to the construction of electrical apparatus having windings of the squirrel cage type, in which conductor bars disposed in inductive relation to a core are Welded at their ends to end connecting members.

This application is a division of applicants co-pending case, Serial No. 859,121, filed Aug. 27, 1914, which latter case broadly covers the article produced by the method described and claimed in this application.

Previous to this time, the conducting bars of windings of the squirrel cage type have been secured to end connecting members by screwing, riveting, soldering or brazing, or by casting the end member integral with the bars, or by suph a welding operation between the individual bars and the end members as requires the presence of a third piece, this piece'being welded to both the bar and the end member, .or a projection therefrom. screwing, riveting, soldering and brazing, as ordinarily practised, are open to mechanical objections in that the union of the parts is not such as sufliciently insures against the connections working loose after a comparatively brief period of operation. Casting of the conductor bars to the end member is open to the objection that such an operation involves the comparatively expensive operation of building a mold about the core with the bars in place therein, and, further, that, unless the bars are unnessarily long, the intense heat developed quite close to the core, 7'. 6., immediately adjacent the inner edge of the east end member, is very liable to injure to electrically weld the third piece to both,

a conductor bar and the end member at the same time, the area of this weld being at least twice the cross-sectional area of the conductor bar.

Prior to this invention, it was considered impossible to apply the simplest form of welding, that is, a direct union of the conductingbars to the connecting members, or extensions therefrom. A welded'connection between the highly conductive bars and the end connecting members, or projections therefrom, produced by the use of a flame has been'found to be impracticable. This results from the fact that, as the heat is applied to the parts to be welded wholly externally. thereof, the external portions of these parts are brought to a welding temperature and beyond this point before the interior parts to be welded can be sufliciently heated, resulting in a union between the two parts wherein the parts, if really welded at all, are welded only along the edge of the contact surfaces, the interior portions of these surfaces being unwelded; and, in any case, the exterior of the parts to be welded age to produce a welding heat throughout I the entire area to be welded, has been found impossible, the reason being that sufiicient current does not flow across the joint between the end of the'bar'and the end connecting member to be welded thereto, if the end connecting member is already welded, or otherwise electrically connected, to one or more bars which are also welded, or otherwise electrically connected, to a second end connecting member to which the bar to be welded is similarly secured. With thi condition present, one or more shunt paths are established about the joint to be made, these shunt paths comprising the end member to be welded, the bar or bars secured thereto, the second end connecting member connected to these bars, and the opposite end of the conductor to be welded. In view of the fact that these shunts comprise paths of high electrical conductivity, it will be apparent that such a considerable portion of the current passes therethrough as precludes the possibility of obtaining sufficient current across the joint to be'welded to bring the parts of the same to a welding temperature without destructive heating of parts of the structure.

It is an object of this invention to provide an improved method of welding a plurality of spaced electrically conductive elements to a plurality of other spaced electrically conductive connecting elements, and an apparatus for practising such method.

It is a further object of this invention to provide an improved method of welding and connecting members to opposite ends of conductor bars inductively associated.

with acore of magnetic material, and an apparatus for practising such method.

These and other objects, such as are in cluded in the scope of the appended claims, are attained by this invention, the various novel featuresof which will appear from A the description and drawings, disclosing one 1 mode of practising sa d lnvention, and W111 be particularly pointed out in the claims.

In the accompanying drawings:

Figure 1 is a broken vertical section through the rotor of asquirrel-cage induction motor embodying the article produced by this invention, showing details of apparatus used in assembling the complete rotor, the section being taken on the plane of the line 1-1 of Fig.2.

Fig. 2 is a broken developed plan view of the rotor shown in part in Fig. 1, showing details of apparatus used in assembling the rotor.

Fig. 3 is a broken vertical section in the plane of the line 33 of Fig. 2.

In the drawings, wherein features of the bars 11, maybe a welded one. This end ring 12 can be welded to the conductor bars 11 without much difliculty, by the use of an apparatus similar to that shown in Figs. 1, 2 and 3. The problem is merely one of passing sufficient current through the joint to be welded to heat the parts thereof, across the full area of the surfaces to be welded, to a welding temperature, at which time pressure applied to these parts will force the same into intimate union. The individual bars are welded separately to the corresponding projections 14 on the end connecting'ring 12.

This apparatus, as shown, comprises a source of current 16, here shown as the secondary of a transformer, and, welding -terminals connected thereto, the terminal 21 being for the'purpose of connecting the end ring to one side of the source 16 and comprising pivoted jaw members 22 and 23 and an adjustable bolt 24 for causing a portion of the ring to be gripped and held in good electrical engagement with the oppositely disposed jaw members. also serve to bind a supply terminal to the welding terminal 21. The terminal 25 comprises pivoted jaw members 26 and 27 and mum. Parallel -members 31 are held in spaced relation and are fixed in position, as by being secured to a fixed support 32. Pivoted jaw members 34 and 35 pass be tween the members 31 and extend into such position that the end of the member 34 lies over the end of the bar to be welded. and the end of the member 35 lies beneath the corresponding extension 14 of the end ring. A cam member 37 is pivoted between the members 31 and is provided with an operating handle 38, and serves to force the member 34 to approach the member 35, the latter being held, and to thus squeeze the end of the conductor bar and the end ring extension to be welded into intimate contact, this cam being operated to produce such effect when the welding current has brought the parts to be welded to a welding heat.

The operation of welding one end ring,

such as 12, to corresponding ends of bars 11,

This bolt 24 may 13, then, this latter welding operation is similar to that described in connection with the welding of the ring 12 to the opposite end of the bar 11,. lVhen, however, the bar 11 is welded to the ring extension 14,, the other end of this bar being already welded to the ring 12, and it is attempted to weld another bar, such as 11 to its corresponding ring projection 14 by the same welding process, the total current flowing between the terminals 21 and 25 divides into two paths, one portion of the current flowing across the engaging surfaces of the parts to be welded, 14 and 11 and another portion of the current flowing through the ring projection 14,, bar 11,, ring 12 and back through the bar 11,, to the terminal 25. 'It will be apparent that it is quite impossible to pass sufficient current across the portion of the bar 11 and the end ring projection 14 to be welded thereto, or, at least, only at the expense of dangerously heating the bar 11 and the body portion of the bar 11 It will be obvious then, that, even were it possible to weld the bar 11 to the ring projection 14 nevertheless, when it is attempted to weld another bar, such as 11,, and the corresponding ring projection 14,, the difiiculties are greatly increased, since there are now two shunt paths about the engaging surfaces of the parts to be welded, and, hence, it is practically impossible to secure enough current to heat the parts to be welded to a welding temperature. As can be readily seen, the number of shunt paths about the parts to be welded, and, hence, the difficulties of welding are increhsed as the number of bars in electrical engagement with the end ring to be welded increases.

In accordance with this invention, means are provided for choking or opposing the flow of any current through the bar to be welded, other than that current which is useful to produce welding heat in the parts to be welded; in other words, the current which, under normal conditions, would flow through the bar to be welded, in shunt to the path of the welding current, is so reduced as to be negligible. As shown in the drawings, an alternating current source may be used for the welding operation, and suitable means may be provided for choking off or opposing any undesirable flow of current in the bar or member to be welded, this means being here shown as a closed magnetic circuit established about the bar to be welded, and of sufficient intensity to effectively choke off any current other than the welding current. When the article to be welded is, as shown in the drawings, a squirrel-cage winding of an induction motor, a piece of iron, or other highly magnetic material 41, is used, this member bridging the core slot occupied by the conductor bar to be welded to the end ring. The effect of this member 41 is to establish a closed magnetic circuit about the bar to be welded which exercises the efi'ect of opposing or choking the flow of alternating current therein, this eitect being similar to the insertion, in the circuit of the body portion of the bar of a source of opposing electromotive force. This opposing or reactive effect may be such as cuts down the useless current flowing in the bar to be welded, to a negligible amount. It will be obvious that where a positive electromotive force is induced by establishing such an intense magnetic field aboutvthe conductor bar being welded as to generate therein a current flowing in the opposite direction, no portion of the current from the welding terminals will pass through the conductor bar at any point other than the portion to be welded.

In the case of induction motor rotors,

where the conductor bars are disposed in slots, the greater part of the required magnetic circuit is already present in the iron of the core and the addition of only sufficient magnetic material, bridging the slot, as forms a closed magnetic path of the required dimensions, reduces the current flowing in the bar to a neglible amount, this magnetic bridge developing such a reactance as prevents the flow of any appreciable amount of welding current in the conductor bar to be welded. It will be obvious that the successive conductor bars may be welded by moving the magnetic bridge 41 so that, during each welding operation, the member 41 oocupies such a position as to effectively bridge the slot of the conductor bar being welded.

It will be apparent that when the article to be welded is not already provided with in such element, other than the current that is useful for heating the portions to be welded.

It will also be apparent that the impedance developed by the closed magnetic path ma be materially increased by increasing the requency of the alternating welding current.

It will be obvious that, in accordance with this invention, the conducting members can be cohesively or autogenously united, as by welding the same together directly, 6. 6., without the use of a connecting member welded to both of the conducting members to be joined, and that this weld, in order to be an efficient one, both mechanically and electrically, need be of no greater cross-sectional area than the cross-sectional area of the welded surface of the smaller one of the welded parts.

It should be understood that it is not desired to be limited to the exact details of construction shown and described, or to the Letters Patent 1. The method of building a cage-like device comprising bars of conducting material and end connecting members disposedatthe ends of said bars which consists in disposing a core of magnetic material within the inner periphery of said bars, completing the magnetic circuit about a given bar to be welded by magnetic material coacting with said core, and passing an alternating current through the point of contact of the bar to be welded and its associated end connecting member.

2. The method of welding the bars of a squirrel cage rotor disposed in the slots of said rotor to the associated end ring which consists in completing a magnetic circuit about the bar'to be welded and passing an alternating current through the point of contact of said barand the end ring.

3. The method of welding the bars of a squirrel cage rotor disposed in the slots of said rotor to the associated end ring which consists in completing a magnetic circuit about the bar to be welded by a member of magnetic material which bridges the gap formed by said slot.

4. In apparatus for electrically welding conductive bars inductively associated with a core of magnetic material to an end ring, a source of alternating welding current, and means to cooperate with the magnetic material of the core for establishing a magnetic field about the bar to be welded of intensity substantially choking off any current in said barother than the useful welding current.

5. In apparatus for electrically welding conductive bars disposed in slots of a' core of a dynamo-electric machine to an end ring, a source of alternating welding current, and means to cooperate with the magnetic material of the core for establishing a magnetic field about the bar to be welded of intensity substantially choking 0H any current in said bar other than the useful welding current.

associated end connected member.

7 The method of building a structure comprising bars of conducting material and end connecting members disposed at the ends of said bars which consists in completing a magnetic circuit about a given bar to be welded, and passing an alternating current through the point of contact of the bar to be welded and its associated end connecting member.

8. The method of constructing a cage-like device comprising bars of conducting material and end connecting members which consists in electrically welding the bars to the end connecting members.

In testimony whereof, the signature of the inventor is affixed hereto.

NATHAN WILKINSON. 

